The manufacture of a metal sheet member is mainly achieved by plastically deforming a blank via an externally applied load, depending on the plastic deformation capability of a metal material. For different metal materials, different forming processes and forming conditions should be adopted.
Since an aluminum alloy, a magnesium alloy, a titanium alloy, and the like materials have low density and high specific strength, and a part of the same mass made from them can provide higher carrying capacity, such a material is referred to as a lightweight material. A common disadvantage of such materials is poor plasticity at room temperature, making it difficult for the materials to manufacture a complex part at room temperature. Currently, a hot forming method is mainly adopted for shaping such materials. That is, a blank to be shaped is heated to an appropriate temperature and then shaped. According to different deformation speeds of the material during forming, the hot forming can be divided into a slow type and a quick type. For example, superplastic forming is a typical slow forming, and high-pressure gas bulging forming is a typical quick forming. The superplastic forming utilizes a relatively low gas pressure (typically lower than 10 atmospheres, i.e., 1.0 MPa) to deform a blank under a high-temperature at a very slow rate, typically at a strain rate lower than 10−2/s. Since a person cannot operate in a high-temperature environment, or a part is stuck to a mold under a high temperature, it should remove the part only after the mold and the part are cooled to a lower temperature upon forming. Therefore, it often takes several hours or even longer to superplastic form a single part. This disadvantage significantly limits application of the superplastic forming in mass production. High-pressure gas bulging forming is achieved by increasing the gas pressure (for example, reaching 10 MPa or even higher) to deform the blank in a relatively short period of time. Since the entire process of the high-pressure gas bulging forming is very quick and the forming cycle of a single part requires only tens of seconds or even shorter, the high-pressure gas bulging forming becomes an advanced technology for mass production using the aforementioned lightweight metal materials. During the high-pressure gas bulging forming, currently a sheet blank is deformed mainly by quickly inflating the cavity of a mold through inflation holes partially disposed on the mold. Since during gas bulging forming both the sheet blank and the mold are at a relatively high temperature, while the introduced gas is in a state of room temperature and high pressure, the temperature of a local region on the blank will be significantly reduced to form a non-uniform temperature field due to the air flow and pressure drop during the inflation process. For a part having a simple shape such as an axisymmetric cylindrical part, the inflation hole often just faces the central position of the sheet blank, such that it can be substantially ensured that the part is deformed in a symmetrical manner. However, for a complicated metal sheet part, if the position of the inflation hole is not set properly, an unreasonable temperature field distribution will be formed on the sheet blank. On the other hand, since the gas is introduced into an enclosed space formed by the sheet blank and the mold cavity through the locally-positioned inflation holes during quick inflation, there may be a certain degree of non-uniformity in the gas pressure within a short period of inflation. Deformation of the metal sheet blank is co-determined by the temperature distribution on the sheet blank and the gas pressure acting on the sheet blank. When the temperature distribution and pressure distribution are unreasonable, it will be difficult to obtain the desired final part.
In order to realize precise and quick forming of a thin-walled metal sheet part having a relatively thin wall thickness and a complex shape, it is necessary to develop a forming technology which can ensure that the blank is deformed under a reasonable temperature condition and a reasonable gas-pressure condition.